If you watch Thai on this
at 4:45 you’ll see him make a little upward snap with his hips as he goes over a rock. This keeps from stalling out on a rock and from hitting your butt.
You need a boat that’s short enough or crammed with enough gear that you can push with your feet and and arch your back to get your BUTT off the BOAT and BOOF.
It’s sort of a pathetic version of the kayaker’s boof, but the idea is similar: getting out and away from an obstacle.